Advertising signs are known in many different shapes, sizes and designs. A common design hitherto has been a sign having a multiplicity of square or triangular shaped prisms, which are arranged to rotate about their axes mounted generally side-by-side with their axes vertically. Each side of the prisms has a vertical strip of a poster or other image mounted on them, and the rotation is synchronized so that all the strips for one image are shown at once to make up a complete image. Thus, for triangular prisms, there can be three different images, which change periodically, as the prisms rotate. For square prisms there can be four different images, with both sides of the sign being visible and displaying different images.
Another type of advertising sign is one that is formed directly of a matrix of light emitting devices, whether of one colour or of several or many different colours. If the matrix is of light sources of a single colour, then they can be controlled to be turned on and off in particular patterns to provide a monochrome advertisement. If there are a large number, particularly if of different colours, then large, self-luminescent advertisements can be produced by programming the controller that controls the switching of the light sources on and off. As light emitting diodes have become available, especially in several colours, this has become a preferred form of the light source for such matrices. Such electronic signs can display either still or moving images. Such signs are not, however, generally double-sided unless two independent such signs are mounted back-to-back.